LEARNING EXPERIENCE

I began reading diesel magazines more than a year ago when I made the decision to become a diesel owner. After all the excitement involved with such an adventure, I fear I may have made a mistake and am reaching out for advice.

I bought a 10-year-old Duramax pickup about a month ago that looked and drove like new and showed absolutely no signs of abuse. It was perfect inside and out. It had a number of mild modifications, such as a cold-air intake and a couple other sensible performance mods. I had only driven the truck about 2,500 miles before a “Check Coolant Level” warning message appeared. I looked in the coolant surge tank and saw that it was a bit low, so I filled the bottle to the “cold fill” line. My adventure was becoming a nightmare.

It seems that coolant was being contaminated with either air or exhaust gases. I instantly thought it was due to a failing head gasket, so I did the usual checks and they came back negative. There is no coolant in the oil, no white smoke out the exhaust, hot and cold cooling system pressure measured 15 psi, and we tested for the presence of exhaust gas in the coolant. None of the tests proved conclusive, so I began reading what I could find online, and most Internet experts

agreed that a head gasket would be the most likely cause of my truck’s symptoms.

I started closely monitoring the truck, and the temperature on the dash gauge began acting in odd ways. It would all of a sudden run high after hard acceleration, and then, while coasting, the engine temperature would settle back into the normal range and stay there.

The other symptom was the truck’s temperature gauge would increase normally to about a quarter of the way then drop to cold, and the heater would blow cold air. I added coolant occasionally, which would blow out of the overflow whenever the cap was removed. Coolant would also be expelled out the overflow tube occasionally, but just a small amount. It appears that cooling system pressure is only rising slightly above the cap’s rated 15 psi, which doesn’t appear to be due to a head gasket problem. I could even drive the truck at normal highway speeds, and it would run fine and stay at a normal temperature.

I changed the lower radiator hose because it had been rubbing on the idler arm. I flushed the cooling system, changed thermostats, and replaced the Oring on the upper coolant pipe that attaches to the thermostat housing (because a dealer suggested it). I installed a new surge tank cap and, of course, bled the cooling system. The air is still there! I have taken it to a few local mechanics. They don’t believe the problem is due to a head gasket, but they also don’t have the enough experience with diesels to tell me what might be causing it.

I don’t really want to pay someone to use my truck as a learning experience. The next closest diesel garage is hours away, and I don’t want to take the chance by driving the truck that far. The dealership techs thought this was similar to what might happen if there was a clogged overflow or a cracked block, which scares me. This entire problem has been one big headache and I have only owned the truck for about 7 weeks.

Ed Larka

Ely, NV

Sorry to hear of your first-diesel experience. Generally, we recommend new prospective diesel owners drive a used (and out of warranty) truck for enough miles to reveal any sort of problem with the engine or drivetrain before writing the check. A diesel engine (any diesel engine) puts a good deal more stress on the head gaskets than does a gas engine. A head gasket failure usually results in a compression/combustion leak between cylinders or a compression/combustion leak into the cooling system. Only the worst head gasket failures result in coolant migrating into a cylinder because combustion pressures can

reach into the thousands of pounds per square inch, while as you noted the cooling system tops out at just 15 psi.

The coolant surge tank cap limits cooling system pressure to a maximum of 15 psi, but normal running pressures should remain in the 3-8psi range. If you’re seeing 15 psi and the radiator hoses remain pretty hard after the truck sits overnight, you can be sure that combustion pressure is finding its way into the cooling system. We’re aware of other instances of Duramax head gasket failures that produced excessive cooling system

pressure, which couldn’t be positively identified by an exhaust gas analyzer.

While we haven’t heard of a Duramax EGR cooler developing a leak that allows exhaust pressure to migrate into the cooling system, we suppose it could happen. However, if your engine’s EGR cooler developed a leak, more exhaust soot would also be present in the coolant. You’d see a dark ring or smudges around the inside of the coolant surge tank. Additionally, exhaust system backpressure, when driving normally, is usually below the pressure found in a cooling system. This

means coolant is more likely to flow through an EGR cooler and into the engine’s exhaust/intake system—not exhaust flowing into the cooling system, and this sort of leak would not necessarily produce excessive pressure in the cooling system.

The cooling system overpressure problem you’re reporting is almost certain to be head gasket related. You’re looking at about $1,000 for new gaskets, head bolts, and miscellaneous materials if you can do the work yourself. It’ll cost about $3,000 or more if you hire the work out. Try to get the previous owner to help; our guess is that

he had to know about it. Good luck, and let us know how it works out.